Faraday rotator as an optical element with a function to rotate the polarization plane of transmitting light is used in optical devices such as optical isolator, optical attenuator, optical circulator and photo-magnetic field sensor for communication. Faraday rotator is generally prepared by using a plane-like bismuth (Bi)-substituted rare-earth iron garnet single crystal. The Bi-substituted rare-earth iron garnet single crystal is prepared by the liquid phase epitaxial (LPE) process as one of flux processes. Single crystals are grown at atmospheric pressure by the flux processes.
In growing the Bi-substituted rare-earth iron garnet single crystal by the solution process such as the flux processes, generally, PbO, Bi2O3 and B2O3 are used as the solvents so as to stably grow such garnet single crystal while the solvents are maintained at their supersaturation states. During the growth of the magnetic garnet single crystal, therefore, a small amount of lead (Pb) contaminates in the resulting crystal. In Faraday rotators for use in optical devices for communication, magnetic garnet single crystals at a Pb content “y” of about 0.03 to 0.06 in the chemical formula Bi3−x−yM1xPbyFe5−z−wM2zM3wO12 have been used conventionally.
Patent Reference 1: JP-A-2001-044026
Patent Reference 2: JP-A-2001-044027.